A conventional reciprocating drive mechanism typically includes one or more connecting rods that translate the rotary movement of a crankshaft into linear, reciprocating movement for driving respective piston rods. A typical connecting rod includes an elongated shaft that terminates at a first longitudinal end in a so-called “big end” having a relatively large, transverse bore formed therethrough for facilitating coupling to a crankshaft. The shaft terminates at a second longitudinal end in a so-called “small end” having a relatively smaller transverse bore formed therethrough for facilitating coupling to a piston or piston rod. The big end and the small end thus define respective, generally annular members at opposing longitudinal ends of the shaft of the connecting rod, each annular member having a proximal side that is connected directly to the shaft and a distal side that is spaced apart from, and not connected directly to, the shaft.
An annular journal bearing is typically shrink-fit within the small end bore of a connecting rod for rotatably engaging a cylindrical crosshead pin that extends therethrough. A film of lubricant can be provided in a small annular gap between the crosshead pin and the journal bearing to ensure smooth rotation of the pieces and to minimize wear. Since the orientation of the journal bearing is fixed relative to the small end of the connecting rod, the journal bearing has a proximal side and a distal side that correspond to the proximal side and distal side of the small end, respectively.
As the connecting rod reciprocates during operation, the small end of the rod and its respective journal bearing rotate about and alternatingly push and pull the crosshead pin that extends transversely therethrough. It has been observed that, during such reciprocation, the small end and the journal bearing may undergo asymmetric deformation. Particularly, when the small end and the journal bearing pull the crosshead pin (i.e., when the connecting rod is in tension), the distal sides of the small end and the journal bearing may deflect or deform away from the crosshead pin due to resistance from the crosshead pin and from the film of lubricant located between the crosshead pin and the distal side of the journal bearing. By contrast, when the small end and the journal bearing push the crosshead pin (i.e., when the connecting rod is in compression), the proximal side of the small end, which is directly connected to and supported by the rigid shaft of the connecting rod, resists deformation. The proximal side of the journal bearing, which is supported by the proximal side of the small end, therefore also resists deformation. Thus, instead of deforming or deflecting away from the crosshead pin, the proximal sides of the small end and the journal bearing overcome the resistance of the lubricant film, causing the gap between the proximal side of the journal bearing and the crosshead pin to be compressed. Some or all of the lubricant in the gap is thereby forced out and the film of lubricant in the gap is thereby thinned or entirely evacuated. Such thinning of the lubricant film can result in excessive and/or uneven wear on the journal bearing and the crosshead pin, which may have a deleterious effect on the reciprocating compressor as a whole.
One attempted solution that has been implemented for mitigating the above-described lubricant thinning is the use of high viscosity lubricants that provide greater resistance against compression. However, the use of such high viscosity lubricants results in increased friction and associated losses in power. Another attempted solution has been to use a larger diameter bearing, but an efficient solution has yet to be achieved.